string seating - was bridge caps

[Richard Brekne]

Ron Nossaman wrote:

> >> During the wet cycle,
> >
> >This sounds great.. could even be exactly whats happening. Or it could be just
> >a compounding factor.
>
> Could be, but I did run an experiment that showed me the bridge surface
> does move up and down the pins with MC changes in the bridge. How about
> doing us one to measure the up force necessary to push a string under, say
> the usual arbitrarily chosen 160lbs tension about 0.010" up a pair of
> bridge pins against 1° downbearing, 10° pin stagger angle, and 20°
> inclination angle. If it's over 1470psi, we'll have a winner. If not, we'll
> be back where we started.
>

I have no doubt that the bridge is moving, what I questioned was whether this was
the reason (or how much of the reason) for the string indentations. As I said, with
positive down bearing it would seem to me the same indentations would come about
anyways. Grin... I suppose you wouldnt mind explaining the significance of 1470 psi
here...:) If you get a chance you might describe your experiment a bit for us.


>
> >Heres the other point that makes me scratch my head....xxx the question
> this fact raises is
> >why doesnt the string conform to the somewhat rounded profile of the bridge ?
>
> Depends on the overall downbearing angle, doesn't it? As the board sinks
> and bearing approaches zero, what happens?
>
>
> >and why then the same string under the same conditions "bend" nicely over the
> >bridge if you simply remove the bridge pins ?
>
> Does it, or is this just speculation?

as long as we have enough positive downbearing.. I cant see how it could escape
from doing so. But I will certainly buy that if there exists a point on the bridge
that is lower then a line drawn between the maximum deflection and the termination
points, then forcing the string down at this point will most definitly create the
problem you described...

>
>
> > I would think that you would have
> >to have a point on the bridge near the edges that was below the level of the
> >front temination point, or the bearing point behind the bridge in order to
> >create what you describe above.
>
> Exactly the point.

I think I see your point well enough. As I understand it thats the basic reasoning
behind seating pins by tapping lightly between the pins. Whatever seating is needed
and / or benificial will be taken care of in this manner. Pressing or tapping
outside the bridgepins risks damaging the bridge as well as quite possibly creating
this temporary situation you describe.

I still see a need to seat strings on bridges tho... but I dont really think the
reasons for this are at odds with your points here.

> >I wonder also if you could explain what you mean by
> >"behind the  (-20°) vertical.
>
> The bridge surface is the horizontal termination, the pin is the vertical,
> only it's not vertical. Any way I could possibly have said this would have
> been challenged by somebody, so I went for literal.

I wasnt really challanging it... just didnt quite get your meaning. Still unclear
as to how this in itself can cause a false beat, if thats what you were saying.

>
> Ron N

What would happen I wonder if you took oversized bridgepins, and notched them
purposely to hold the string in place vertically....grin..

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no